(1) Field of the Invention
The present invention relates to an optical module, for example, the present invention relates to an art that is preferably used for an optical module for pluggable optical communication serving to transmit and receive mainly a signal not less than 10 Gb/s (giga bit per second).
(2) Description of the Related Art
In a transceiver module for optical communication, as a mode that is compact and can be easily replaced, a plugable module having both of optical and electric connecter interfaces (IF) is required. FIG. 11 shows an external view of an entire XFP module in conformity with an XFP (10 Gigabit small Form Factor Pluggable)—MSA (Multi-Source Agreement), which is one of conventional pluggable transceiver modules.
In this FIG. 11, a reference numeral 100 denotes an XFP module and the XFP module 100 is detachably mounted on a host board (also referred to as a mother board) 200 by inserting a plug portion 101 of the XFP module 100 into a connector interface 201a of a cage part 201 to be mounted on the mother board 200 through an opening portion 205 that is provided on a bezel part 204 of the mother board 200l. In addition, at one end opposite to the plug portion 101 of the XFP module 100, a receptacle part 110a with connector holes 113 and 114 into which an optical connector plug for an optical fiber is detachably inserted and connected is provided. In the meantime, in FIG. 11, a reference numeral 202 denotes a heat sink for cooling the cage part 201, and a reference numeral 203 denotes a clip for fixing this heat sink 202 on the cage part 201, respectively, and in FIG. 11, these cage part 201, heat sink 202, and clip 203 are decomposed.
Then, FIG. 10(A) is a schematic plan view showing an inner structure of the above-described XFP module 100. FIG. 10(B) is an A arrow side view in FIG. 10(A). Also described in patent documents 1 and 2 to be described later, the XFP module 100 shown in FIGS. 10(A) and 10(B) is configured so as to include an optical transmitting device (TOSA: Transmitter Optical Sub-Assembly) 301, an optical receiving device (ROSA: Receiver Optical Sub-Assembly) 302, and a print circuit board 120 in a case (an optical module mechanism) 110 having a receptacle part 110a in which the above-described connector holes 113 and 114 are formed as its basic construction.
The optical transmitting device 301 has a photoelectric conversion element such as a laser diode (LD) or the like, and the optical receiving device 302 has a photoelectric conversion element such as a photo diode (PD) or the like. Both of them are structured as a CAN type (a coaxial package) device or the like having an optical connecter interface in place of an optical fiber. These optical transmitting device 301 and optical receiving device 302 are fixed by a bonding agent or the like to optical device support and fixing parts 111 and 112 in which respective neck portions 301a and 302a are arranged in parallel on the same plane in the receptacle part 110a so as to be fixed in the case 110 while securing a center accuracy by the necessity to secure the center accuracy (a positional tolerance not more than ±25 μm: refer to an arrow 400 in FIG. 10(A)) of the optical connector interface.
The print circuit board 120 has a width that is slightly shorter than the width of the case 110 and a length that is slightly longer than the length from a position in adjacent to an end surface opposed to the neck portions 301a and 302a of the above-described respective optical devices 301 and 302 to the plug portion 101 of the case 110. On a surface of the print circuit board 120, an electronic circuit device group including a transmitting circuit (IC chip) 121 for the optical transmitting device 301 and a receiving circuit (IC chip) 122 for the optical receiving device 302 or the like is appropriately mounted.
This print circuit board 120 is positioned and fixed at a predetermined position in the case 110 by a fixing screw 150. In this case, the end portion at the side of the plug portion 101 of the print circuit board 120 served as a card edge connecter part 120a to be inserted and connected into the connector interface 201a of the above-described cage part 201, so that the tolerance of the outside dimension of the print circuit board 120 is needed to be, for example, not more than ±50 μm (refer to a reference numeral 600 of FIG. 10(B)).
In the meantime, in the card edge connecter part 120a, a wiring 120b for supplying a power source from the side of the mother board 200 to the print circuit board 120 and for transmitting and receiving a signal between the print circuit board 120 and the mother board 200 is formed. In addition, in FIG. 10(B), in order to make connection operation with respective optical devices 301 and 302 easily, it is general that the print circuit board 120 is fixed so as to be located lower than a plane including center axes of respective optical devices 301 and 302.
On the other hand, the end portions at the sides of respective optical transmitting device 301 and optical receiving device 302 of the print circuit board 120 are connected to the optical devices 301 and 302 by flexible substrates 130 and 140, and thereby, the optical transmitting device 301 is electrically connected with the optical transmitting circuit 121, and further, the optical receiving device 302 is electrically connected with the optical receiving circuit 122. In the meantime, in FIG. 10(B), respective end portions of the flexible substrates 130 and 140 are directly connected to the end surfaces of the optical transmitting device 301 and the optical receiving device 302, however, as shown in FIG. 7 and FIG. 15 of the patent document 2, respective end portions of the flexible substrates 130 and 140 may be indirectly connected to the end surfaces of the optical transmitting device 301 and the optical receiving device 302 via a ceramic substrate for connection of a flexible substrate that is provided at the sides of respective optical devices 301 and 302.
Thus, by using the flexible substrates 130 and 140 to connect respective optical devices 301 and 302 with the print circuit board 120, a signal of 10 Gb/s is transmitted on a transmission line formed on the flexible substrate 120, so that it is possible to realize connection with less deterioration of waveform. In addition, it is also possible to absorb a positional deviation in a longitudinal direction between the optical devices 301, 302 and the print circuit board 120 (each of the tolerance of the outside dimension of the print circuit board 120 and the optical device 301, 302) by flexibility of the flexible substrate 120.
In addition, according to an prior art proposed by the following patent document 3 (an optical transmission module incorporated active connector), it is described that the flexible print circuit having an electric part such as a resistance, a transmission IC, and a reception IC or the like mounted thereon is mounted with bent in a predetermined shape in a cylindrical case. Therefore, on the flexible print circuit board described in the patent document 3, cutting and score are provided so as to be bent at a predetermined shape.    Japanese Patent Laid-Open No. 2002-353471    Japanese Patent Laid-Open No. 2003-249711    Japanese Patent Laid-Open No. SHO62-019812
However, according to the module structure described above with reference to FIG. 10(A) and FIG. 10(B), it is possible in some degree to secure the tolerance of the outside dimension of the print circuit board (not more than ±50 μm: refer to a reference numeral 600 in FIG. 10(B)) by absorbing the positional deviation in a longitudinal direction in the optical module mechanism 110 with the flexible substrates 130 and 140, however, as shown by two-head arrow 400 in FIG. 10(A), if deviation not less than ±400 μm at an interval between the optical devices 301 and 302 is generated due to the coaxial deviation of the optical devices 301 and 302 (the positional deviation of the neck portions 301a, 302a and coaxial portions 301b, 302b), it becomes very difficult to correct the position (to absorb the positional deviation) at the flexible substrates 130 and 140. In addition, due to a large size of the print circuit board 120 (it shares a large portion of a mounted area in the case 110), it is also difficult to realize the positional accuracy of the print circuit board 120 and the optical devices 301, 302.
In other words, according to such conventional structure, since it is not possible to absorb the positional deviation (the positional deviation in a twist direction) due to the positional deviation in a width direction of the optical module mechanism 110 of respective optical devices 301, 302 and the print circuit board 120; the rotations about center axes of the coaxial portions 301b and 302b of the optical devices 301 and 302; and the deviation of the print circuit board 120 in the optical module mechanism 110 or the like, it is difficult to secure the enough positional accuracy. As a result, it takes a long period of time for a module assembling step. This is the same as the structure that is proposed in the patent documents 1 to 3.
In addition, according to the structure to connect the optical devices 301, 302 with the print circuit board 120 by the flexible substrates 130 and 140, due to absorption of the above-described positional deviation in a longitudinal direction, there is a limitation in making connection lengths between the optical transmitting device 301 and the optical transmitting circuit 121 and between the optical receiving device 302 and the optical receiving circuit 122. When treating a super fast signal not less than 40 Gb/s, a deviation occurs in a waveform of transmitted and received signals to cause deviation of optical transmitted and received properties. Further, the optical transmitting circuit 121 and the optical receiving circuit 122 are mounted on the same print circuit board 120, so that this involves a problem that a cross talk between transmission and reception via the print circuit board 120 is generated (refer to a reference numeral 500 in FIG. 10(A)) to deteriorate the reception sensitivity.